Curupaity
Curupaity is the name of a defensive area in the perimeter of the Humaita Fortress. It consisted of fortified lines of trenches and moats covered with artillery. This area also protected Humaita from a land attack The importance of the fortress is derived both from its position in a strategic point on the Paraguay River and as a passage to the north.
After the Battle of Tuyuty, the Allies slowly began to manage a large movement to encircle the fortress.
From that point López launched continuous  attacks in order to keep the enemy under pressure. Many skirmishes took place between late May and August, 1866. In those actions both the allies and the Paraguayans suffered  thousands of casulaties. Some sources affirm that the allies' losses may have reached  5,000 to 8,000 men in this period.
One kilometer ahead of Curupaity stood Curuzu, the first line of trenches that protected the fortress. On this place there would happen a battle that can be understood as a foretoken struggle of a major engagement.
In fact, the Allies were preparing to sent troops to land in Curuzu since July. After his return to the bulk of the army, Antonio Paranhos, Viscount of Porto Alegre, was designated by Mitre to led the forces on this attack . He would command the II Corps of the Brazilian Army, which numbered 14,000, in a attempt to take the trenches of Curuzu. The Imperial Navy under Admiral Joaquim Marques Lisboa, Baron of Tamandaré would support the operation both by firing on the Paraguayan trenches and making the landing.
In Curuzu, General Díaz, for some López' most capable officer, was in command of 2,500 troops in three battalions. As reinforcement he had received just a battery of three cannons and some small detachments. Outnumbered in a proportion of almost six to one he had to hold the position with twelve cannons and mortars.
On September 2, the Allied Fleet, consisting of some twenty ships, begins to pour fire on Diaz' trenches. As soon as the transports landed the troops on the field Porto Alegre arranged for the assault on Curuzu. He deployed his troops in a frontal attack formation. The fire coming from the trenches was resolute and as the fight progressed the II Corps was obliged to managed in order to flank the position.
On the river, the ships were facing opposition of artillery coming from Curupaity and Curuzu. The Paraguayans were also using torpedoes (as mines were called) to menace the fleet. On the night of the first day, the 6-gun steamship Rio de Janeiro was severed hit by artillery. Some ships that came to aid the steamship soon came under fire of Curupaity. One of these ships, the gunboat Ivahy, had it engines hit and had to withdraw. Four of its crewman were injured. The morning of next day, two torpedoes  sank the Rio de Janeiro. One officer was killed and seven sailors were wounded.
The attack onto Curuzu was undertaken by the II Corps of the Imperial Army
Notwithstanding by the afternoon Díaz could not keep the enemy out of the trenches anymore. The Allies entered Curuzu and after a hand to hand fight they took control of the trenches. The remaining Paraguayan troops moved  to Curupaity.
In Curuzu both sides experienced, in a approximating, the same amount of casualties. The 2nd Corps had 159 men killed and 629 wounded, while the Paraguayans had 800 casualties.
After Curuzu was taken, the Allied Command became optimistic in respect of the attack on Curupaity.
Troops were brought from Tuyuty until they performed a force of some 20,000 men. Artillery was being gathered to support the attack and the navy added new ships to pour fire onto Curupaity.
Meantime, López ordered the reinforcement of the Paraguayan positions in Curupaity. A new line of trenches and a moat were been built and new artillery pieces were brought. The Allies did not notice the new fortified positions.
On September 12, however, a controversial event took place. After Curuzu, López sent Mitre a message of truce. He wanted to parley. Known as Yatayti-Corá, this encounter has many different versions. For some it was López' last attempt of reaching peace. For others it was just a way he planned to gain time until his positions were strong enough to face the Allied attack.
The Allies used Curuzu as a footstep in their next  against Curupaity - by Candido Lopez (Fine-Arts Museum/ Buenos Aires)
As far as we know, López first asked to parley with Mitre alone. They met each other on the middle of the war zone, between the two enemy armies. As the talks progressed, Mitre called for Flores and the new Brazilian Army Commander, General Polidoro Jordão. While the former accepted to talk, Polidoro refused to take part in the encounter. We do not know if the Allies were intransigent or López was not ready to make concessions. The fact is that Yataity-Corá failed and the hostilities went on.
The navy started the bombardment of Curupaity shortly after dawn of the  22th. Among the vessels there were four ironclad steamships. In response, 49 cannons started sending fire from the Paraguayan stronghold.
Departing from Curuzu, at 12 AM, the Allied Army launched the attack. According to many authors,  the force was deployed in four columns. Only SCHNEIDER (see bibliography) cites a fifth column, made-up of Uruguayans. He puts it on the centre of the Allied formation.
Nevertheless, we will describe  here the view of the majority.
On the left the Imperial Army and to the right the Argentinean troops. The extreme left was led by Colonel Augusto Caldas, under whom there were many units of the National Guard. To his right, General Albino de Carvalho marched with six Infantry Battalions and some Cavalry units.  On the right, General Wenceslao Paunero with twelve Argentinean Battalions. Finally, on the extreme right, General Emílio Mitre (presidente Mitre's brother) led five battalions. The 16th Volunteer Battalion of the Imperial Army was deployed along the river bank to fire onto the Paraguayan stronghold.
López'  5,000 strong in Curupaity were positioned in two lines of trenches with a moat ahead of each of them. They set the artillery pieces at their disposal in two lines of defense. Díaz would command the troops under attack.
The second line of trench was built on a hill so that from the Allies position it could not be seen. Thus, they presumed that they would deal with only one line of defense.
As the mass of the enemy army came, the Paraguayans on the first trench shot a barrage of volleys on them. The moat retarded the advance and many soldiers could not pass this first obstacle.
Meanwhile, the fleet tried to back the advance, but at the same time the ships had to keep some distance from the powerful guns of Humaitá. That meant a weak support for the operation.
Even with little support, the Allies reached the first line of the defensive perimeter. Only then they knew that the enemy had constructed a second line of defense. They stunned for a moment trying to wonder what to do. When Mitre received the news he ordered his troops not to stop the advance. To make things less worthy, before the Allies took the trench Diaz' men had positioned the cannons on the second line. Until 4 PM the Triple Alliance Forces tried to take control over Curupaity, but the moat and the Paraguayan fire proved to be too much for them. Then came the retreat.
The Allies failed to dislodge the Paraguayan position. Besides, the losses were immense.
The Paraguayan sources claimed a total of 9,000 casualties on the Allied Forces. Nowadays this number is considered exaggerated. Notwithstanding, even the Allies considered the operation a disaster. The casualties counted in some 4,193 according to Brazilian sources, but this number does not include the Uruguayan losses.  The casualties may have totaled 5,000 men.
The Imperial Army in Curupaity had 408 killed; 1,543 wounded and 10 missing. The Navy had 1 killed and 34 wounded. The 16th Volunteer, which saw little action in the assault, suffered 3 dead and 12 wounded.
The Argentinean, for their turn, sustained 587 dead; 1,439 wounded and 156 missing.
During the action 13 commanders of battalion were killed (5 Argentineans and 8 Brazilians).
More than 20% of the initial force was lost.
The Paraguayan Army suffered 54 casualties. Only two officers were killed (a Major and a Lieutenant).
The defeat on Curupaity undermined the Allied High Command. Tamandaré was accused of not giving the proper support to the operation. The Brazilian officers were even more doubtful of Mitre's capability of command. Flores was resentful of the lack of prestige he believe he deserved.
In some weeks Mitre would leave the theater of operations in order to take care of internal problems in the Argentinean Provinces. From this point the Argentinean Army on Paraguay would rest on a force of some 4,000 troops.
Flores returned to Montevideo. He would never return to the battlefield again. The Uruguayan troops left counted no more than 200 soldiers.
The war became a business between Brazil and Paraguay.
Battle of Curupaity  (detail) by Candido Lopez-  Fine-Arts Museum (Argentina)
Humaitá